Part 1

Produced by R. L. Garnett

A LECTURE ON THE PRESERVATION OF HEALTH.

BY T. GARNETT, M.D. Professor of Natural Philosophy and Chemistry in the Royal Institution of Great Britain &c.

SECOND EDITION.

Such the reward of rude and sober life; Of labour such. By health the peasant's toil Is well repaid; if exercise were pain Indeed, and temperance pain. Armstrong.

LONDON: PRINTED FOR T. CADELL, JUNIOR, AND W. DAVIES, STRAND. 1800. (R. NOBLE, Printer, Old Bailey.)

To ERASMUS DARWIN, M.D.

Dear Sir,

THE first edition of this pamphlet having been introduced to the world under the sanction of your name, I take the liberty of prefixing it to the second; and am happy in having another public opportunity of expressing my thanks for the high gratification and instruction which I have received from the perusal of your medical and philosophical works.

I am, Dear Sir, With much esteem, Your very obedient servant,

THO. GARNETT.

Royal Institution, April 8th, 1800.

PREFACE.

Most medical gentlemen will, it is supposed, agree that the greater part of the numerous train of diseases to which their patients are subject, have been brought on by improper conduct and imprudence. That this conduct often proceeds from ignorance of its bad effects, may be presumed; for though it cannot be denied that some persons are perfectly regardless with respect to their health, yet the great mass of mankind are too sensible of the enjoyment and loss of this greatest of blessings, to run headlong into danger with their eyes open.

It was with the hope of making the laws of life more generally known, and better understood, and from thence deducing such rules for the preservation of health, as would be evident to every capacity, that the author was induced to deliver this lecture. It has been honoured with the attention of numerous audiences, in some of the most populous towns in England, where it has generally been read for the benefit of charitable institutions.

The author flatters himself, that besides the benefit produced by his humble endeavours to serve these institutions, those endeavours have not totally failed in the grand object of preserving health; and with the hope that the influence of the precepts here given, may be farther extended, he has concurred in the ideas of those who have advised the publication of this lecture.

It is to be feared, that notwithstanding all which can be done, disease will continue to be a heavy tax, which civilized society must pay for its comforts; and the valetudinarian will often be tempted to envy the savage the strength and soundness of his constitution. Much however may be done towards the prevention of a number of diseases. If this lecture should contribute to the attainment of so desirable an end, it will afford the highest gratification to the author.

The first part of the lecture is the substance of an essay which was read by the author before the Royal Medical Society of Edinburgh, intended as a defence of the general principles of the system of Dr. Brown, whose pupil he then was. It was, according to custom, transcribed into the books of the society, and the public have now an opportunity of judging how far Dr. Girtanner, in his first essay published in the Journal de Physique, about two years after, in which he gives the theory as his own, without the least acknowledgment to the much injured and unfortunate author of the Elementa Medicinae, has borrowed from this essay.

In public lectures, novelty is not to be expected, the principal object of the lecturer being to place in a proper point of view, what has been before discovered. The author has therefore freely availed himself of the labours of others, particularly of the popular publications of Dr. Beddoes, which he takes this opportunity of acknowledging.

This lecture is published almost verbatim as it was delivered. On this account the experiments mentioned are not minutely described, the reader being supposed to see them performed.

* * * * *

A LECTURE, &c.

THE greatest blessing we enjoy is health, without it, wealth, honors, and every other consideration, would be insipid, and even irksome; the preservation of this state therefore, naturally concerns us all. In this lecture, I shall not attempt to teach you to become your own physicians, for when the barriers of health are once broken down, and disease has established itself, it requires the deepest attention, and an accurate acquaintance with the extensive science of medicine, to combat it; to attain this knowledge demands the labour of years. But, a majority of the diseases to which we are subject, are the effects of our own ignorance or imprudence, and it is often very easy to prevent them; mere precepts however, have seldom much effect, unless the reasoning upon them be rendered evident; on this account, I shall first endeavour, in as plain and easy a manner as possible, to explain to you the laws by which life is governed; and when we see in what health consists, we shall be better enabled to take such methods as may preserve it. Health is the easy and pleasant exercise of all the functions of the body and mind; and disease consists in the uneasy and disproportioned exercise of all, or some of the functions.

When dead matter acts upon dead matter, the only effects we perceive are mechanical, or chemical; for though there may appear to be other kinds of attraction, or repulsion, such as electric and magnetic, yet these come under the head of mechanical attraction, as producing motion; we may therefore lay it down as a law, that when dead, or inanimate bodies act upon each other, no other than mechanical, or chemical effects are produced; that is, either motion, or the decomposition, and new combination of their parts. If one ball strike another, it communicates to it a certain quantity of motion, this is called mechanical action; and if a quantity of salt, or sugar, be put into water, the particles of the salt or sugar will separate from each other, and join themselves to the particles of the water; the salt and water in these instances, are said to act on each other chemically; and in all cases whatever, in which inanimate, or dead bodies act on each other, the effects produced are, motion, or chemical attraction.

But, when dead matter acts on those bodies which we call living, the effects are much different; let us take for example a very simple instance.--Snakes, at least some species of them, pass the winter in a torpid state, which has all the appearance of death; now heat, if applied to dead matter, will only produce motion, or chemical combination; but if it be applied to the snake, let us see what will be the consequence; the reptile first begins to move, and opens its eyes and mouth; when the heat has been applied for some time, it crawls about in search of food, and performs all the functions of life. Here then, dead matter, when applied to a living body, produces living functions; for if the heat had not been applied, the snake would have continued senseless, and apparently lifeless. In more perfect animals, the effects produced by the action of dead matter on them, are more numerous, and are different in different living systems, but are in general the following--sense and motion in almost all animals, and in many the power of thinking, and other affections of the mind. The powers, or dead matters, which are applied, and which produce these functions, are chiefly, heat, food, and air. The proof that these powers do produce the living functions, is in my opinion a very convincing one, namely, that when their actions are suspended, the living functions cease; take away, for instance, heat, air, and food from animals, and they soon become dead matter, and it is not necessary that an animal should be deprived of all these to put a stop to the living functions; if any one of them be taken away, the body sooner or later becomes dead matter: it is found by experience, that if a man be deprived of air, he dies in about three or four minutes; for instance, if he be immersed under water; if he be deprived of heat, or in other words, exposed to a very severe degree of cold, he likewise soon dies; or if he be deprived of food, his death is equally certain, though more slow. It is sufficiently evident then, that the living functions are owing to the action of these external powers upon the body. What I have here said, is not confined to animals, but the living functions of vegetables are likewise caused by the action of dead matter upon them. The dead matters, which by their action produce these functions, are principally heat, moisture, light, and air. It clearly follows therefore, from what I have said, that living bodies must have some property different from dead matter, which renders them capable of being acted upon by these external powers, so as to produce the living functions; for if they had not, the only effects which these powers could produce, would be mechanical, or chemical. Though we know not exactly in what this property consists, or in what manner it is acted on, yet we see, that when bodies are possessed of it, they become capable of being acted upon by external powers, and thus the living functions are produced; we shall therefore call this property excitability, and in using this term it is necessary to mention, that I mean only to express a fact, without the least intention of pointing out the nature of that property which distinguishes living from dead matter, and in this we have the example of the great Newton, who called the property which causes bodies in certain situations to approach each other, gravitation, without in the least hinting at its nature; yet, though he knew not what gravitation was, he investigated the laws by which bodies were acted on by it, in the same manner, though we are ignorant of excitability, or the nature of that property which distinguishes living from dead matter, we can investigate the laws by which dead matter acts on living bodies through this medium. We know not what magnetic attraction is, and yet we can investigate its laws; the same holds good with regard to electricity; if we ever should attain a knowledge of the nature of this property, it would make no alteration in the laws which we had before discovered.

I shall now proceed to the investigation of the laws by which the excitability is acted on; but I must first define some terms which it will be necessary to use, to avoid circumlocution, and at the same time to give us more distinct ideas on the subject.

When the excitability is in such a state as to be very susceptible of the action of external powers, I shall call it abundant, or accumulated; but when it is found not very capable of receiving their action, I shall say, it is deficient, or exhausted. I would not wish however, to have it thought, that by these terms I mean in the least to hint at the nature of excitability, nor that it is really one while increased, and at another diminished in quantity, for the abstract question is in no shape considered; we know not whether the excitability, or the vital principle, depends on a particular arrangement of matter, or from whatever cause it may originate; by the terms here used, I mean only to say, that the excitability is easily acted on when I call it abundant, or accumulated; at other times the living body is with more difficulty excited, and then I say, the vital principle is deficient, or exhausted.

The laws by which external powers act on living bodies, will, on a careful examination, be found to be the following--